A communication system provides a manner by which information formed at a source location can be transferred to a destination location. To effectuate such transfer of information, a communication system is formed, at a minimum, by a sending station and a receiving station interconnected by a communication channel. The communication channel forms a communication link between the sending station and the receiving station. The sending station includes circuitry for converting the information which is to be communicated to the receiving station. Such circuitry forms a communication signal which is communicated upon the communication channel to the receiving station. And, the receiving station includes circuitry for receiving the communication signal transmitted by the sending station and for recovering the informational content thereof.
A wireline, telephone system is a type of communication system. PSTNs (Public Switched Telephone Networks) form the infrastructure of a wireline telephone system. Conventional telephones, or other wireline devices, are coupled to a PSTN by way of wireline connections. Both voice and data communications can be communicated by way of such a telephonic system. PSTNs have been installed throughout significant portions of the world. Telephonic communications effectuated therethrough are widely utilized.
A radio communication system is a communication system in which the communication link formed between the sending and receiving stations is formed of a portion of the electromagnetic frequency spectrum. A wireline connection is not required to form a communication channel interconnecting the sending and receiving stations. A radio communication system is therefore particularly advantageously utilized when a wireline connection between the sending and receiving stations is unavailable.
A cellular communication system is a type of radio communication system. Analogous to the telephonic communications permitted pursuant to a wireline telephonic system, telephonic communications are also permitted pursuant to a cellular communication system. The infrastructure of a cellular communication system is coupled to a PSTN. But, radio connections with mobile terminals obviate the need to install wireline connections to effectuate communications with such terminals.
The mobility permitted when communicating by way of a cellular communication system is much greater than that permitted when a wireline connection is required to effectuate communications. Due in part to the increased mobility of communications permitted by a cellular communication system, use of a cellular communication system to communicate telephonically has become increasingly popular.
Attempts have been made to increase the communication capacity of a cellular communication system. By increasing the communication capacity of a cellular communication system, increased numbers of users are permitted to communicate by way of such a system.
Some cellular communication systems have been implemented using digital technologies. In a digital communication system, the information which is to be communicated is digitized. Once the information is digitized, a communication signal formed therefrom can be transmitted in a bit stream. Two or more communication signals can be thereby multiplexed together by way of a selected, access technique. For instance, time-division-multiple-access (TDMA) communication systems utilize sequential multiplexing of bursts upon a carrier. The bursts are transmitted during selected time slots of frames formed of a plurality of time slots.
The GSM (Global System for Mobile communications) cellular communication system is exemplary of a digital cellular communication system. GSM communication systems have been installed throughout significant areas in which cellular communications are provided.
As noted above, cellular communication systems are popular in many instances due to the increased mobility of communications permitted therein. In some areas, also, access to conventional, wireline telephonic service is unavailable or limited. The costs associated with installing the wireline infrastructure required of conventional wireline systems are significant. In areas in which such wireline infrastructure has not already been installed, the installation instead of a cellular communication system is a cost-effective alternative.
Therefore, in areas in which the existing infrastructure of conventional wireline systems have not already been installed, it is anticipated that installation of cellular communication systems shall instead be made. Telephonic communication shall, in such instance, be effectuated by way of a cellular communication system.
Most simply, a cellular transceiver can be used to effectuate the telephonic communications. However, many communication devices are constructed for connection to a conventional, wireline system. Connection of such communication devices to a cellular transceiver permits such communication devices to be continued to be used even when a wireline system is otherwise unavailable.
Fixed cellular terminals have been developed which permit the connection thereto of one or more communication devices. Conventional, wireline telephones are exemplary of such communication devices. Normal telephonic communication is permitted of a user utilizing the conventional telephone. Communication signals provided to the fixed cellular terminal from the conventional telephone are transmitted by the fixed cellular terminal to the cellular network infrastructure of the cellular communication system. Downlink signals transmitted from the cellular network to the fixed cellular terminal are, in turn, provided to the conventional telephone.
Most normal, telephonic communications are permitted by way of a fixed cellular terminal. However, when the fixed cellular terminal is a digital cellular transceiver, such as a GSM cellular transceiver, DTMF signals generated at the conventional, wireline telephone are not necessarily accurately communicated by way of the cellular transceiver. DTMF signals are generated by a user of the conventional, wireline telephone when carrying out any of many telephonic functions. Generation of the DTMF signals are required, for instance, to gain entry into, and to make use of, many automated telephone services.
In a digital transceiver, an input speech signal is encoded using a vocoder. The vocoder used in a GSM cellular transceiver, for instance, does not guarantee waveform integrity of a signal applied thereto. As a result, accurate encoding of a DTMF signal in a manner to accurately ensure its subsequent recreation cannot be guaranteed.
When a GSM cellular transceiver, or other digital transceiver, forms a standalone device, actuation of a telephonic key actually causes the generation of a code instead of a DTMF signal. The code is transmitted to, and received at, the cellular network. A DTMF signal is created responsive to the received code. Thereby, problems associated with the inability of the vocoder to encode accurately a DTMF signal are avoided. However, when the transceiver is coupled to a separate wireline telephone, or other wireline device, DTMF signals are applied as inputs to the GSM cellular, or other digital, transceiver.
A manner by which a DTMF signal generated by a conventional, wireline telephone, or other device, could be converted into a form to permit the digital cellular transceiver to communicate accurately an indication of the DTMF signal would therefore be advantageous. Use of a fixed cellular terminal to effectuate telephonic communications would thereby more closely resemble that of a conventional, wireline telephonic network.
More generally, a manner by which to convert an inband signal into a form to permit a digital transmitter to communicate accurately an indication of the inband signal would be advantageous. An inband signal is a signal which is transmitted within a channel upon which a signal of another signal-type is transmitted.
It is in light of this background information related to telephonic communications that the significant improvements of the present invention have resulted.